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go/test/escape_struct_return.go

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cmd/internal/gc: improve flow of input params to output params This includes the following information in the per-function summary: outK = paramJ encoded in outK bits for paramJ outK = *paramJ encoded in outK bits for paramJ heap = paramJ EscHeap heap = *paramJ EscContentEscapes Note that (currently) if the address of a parameter is taken and returned, necessarily a heap allocation occurred to contain that reference, and the heap can never refer to stack, therefore the parameter and everything downstream from it escapes to the heap. The per-function summary information now has a tuneable number of bits (2 is probably noticeably better than 1, 3 is likely overkill, but it is now easy to check and the -m debugging output includes information that allows you to figure out if more would be better.) A new test was added to check pointer flow through struct-typed and *struct-typed parameters and returns; some of these are sensitive to the number of summary bits, and ought to yield better results with a more competent escape analysis algorithm. Another new test checks (some) correctness with array parameters, results, and operations. The old analysis inferred a piece of plan9 runtime was non-escaping by counteracting overconservative analysis with buggy analysis; with the bug fixed, the result was too conservative (and it's not easy to fix in this framework) so the source code was tweaked to get the desired result. A test was added against the discovered bug. The escape analysis was further improved splitting the "level" into 3 parts, one tracking the conventional "level" and the other two computing the highest-level-suffix-from-copy, which is used to generally model the cancelling effect of indirection applied to address-of. With the improved escape analysis enabled, it was necessary to modify one of the runtime tests because it now attempts to allocate too much on the (small, fixed-size) G0 (system) stack and this failed the test. Compiling src/std after touching src/runtime/*.go with -m logging turned on shows 420 fewer heap allocation sites (10538 vs 10968). Profiling allocations in src/html/template with for i in {1..5} ; do go tool 6g -memprofile=mastx.${i}.prof -memprofilerate=1 *.go; go tool pprof -alloc_objects -text mastx.${i}.prof ; done showed a 15% reduction in allocations performed by the compiler. Update #3753 Update #4720 Fixes #10466 Change-Id: I0fd97d5f5ac527b45f49e2218d158a6e89951432 Reviewed-on: https://go-review.googlesource.com/8202 Run-TryBot: David Chase <drchase@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Russ Cox <rsc@golang.org>
2015-03-26 14:36:15 -06:00
// errorcheck -0 -m -l
// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Test escape analysis for function parameters.
package foo
var Ssink *string
type U struct {
_sp *string
_spp **string
}
func A(sp *string, spp **string) U { // ERROR "leaking param: sp to result ~r2 level=0$" "leaking param: spp to result ~r2 level=0$"
return U{sp, spp}
}
func B(spp **string) U { // ERROR "leaking param: spp to result ~r1 level=0$" "leaking param: spp to result ~r1 level=1$"
return U{*spp, spp}
}
func tA1() {
s := "cat"
sp := &s // ERROR "tA1 &s does not escape$"
spp := &sp // ERROR "tA1 &sp does not escape$"
u := A(sp, spp)
_ = u
println(s)
}
func tA2() {
s := "cat"
sp := &s // ERROR "tA2 &s does not escape$"
spp := &sp // ERROR "tA2 &sp does not escape$"
u := A(sp, spp)
println(*u._sp)
}
func tA3() {
s := "cat"
sp := &s // ERROR "tA3 &s does not escape$"
spp := &sp // ERROR "tA3 &sp does not escape$"
u := A(sp, spp)
println(**u._spp)
}
func tB1() {
s := "cat"
sp := &s // ERROR "tB1 &s does not escape$"
spp := &sp // ERROR "tB1 &sp does not escape$"
u := B(spp)
_ = u
println(s)
}
func tB2() {
s := "cat"
sp := &s // ERROR "tB2 &s does not escape$"
spp := &sp // ERROR "tB2 &sp does not escape$"
u := B(spp)
println(*u._sp)
}
func tB3() {
s := "cat"
sp := &s // ERROR "tB3 &s does not escape$"
spp := &sp // ERROR "tB3 &sp does not escape$"
u := B(spp)
println(**u._spp)
}